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Abstract

Introduction

Ectopic thymoma is a rare neoplasm, which can be developed in various sites, with
the lung being amongst the rarest.

Case presentation

In this paper, we present the case of a woman with a slow-growing ectopic thymoma,
stemming from the visceral pleura of the upper lobe of the left lung anteriorly, extending
into the left lung and the cardiac wall, invading the fatty tissue near the pericardium,
notably without infiltrating the lung or cardiac parenchyma. The thymoma was successfully
removed via thoracotomy.

Conclusion

Ectopic thymoma is an uncommon neoplasm. To our knowledge, a case of an ectopic thymoma
stemming from the visceral pleura of the lung is extremely rare.

Introduction

Although the vast majority of thymomas are located in the anterior mediastinum (90%),
there have been many sites of ectopic localization of thymomas described. Ectopic
thymomas have been found in the middle and the posterior mediastinum, the neck, the
base of the skull, the pericardium, the lung parenchyma, and the pleural cavity [1-5]; whereas in the visceral pleura are extremely uncommon [6]. In this report, we present a rare case of an asymptomatic female with an ectopic
thymoma stemming from the visceral pleura of the left lung.

Case presentation

In April 2007, a 40-year-old Caucasian woman admitted into our clinic for performing
an orthopaedic operation. The chest x-ray, which is amongst the routine pro-operating
exams preceding a surgery, revealed an asymptomatic left paramediastinal mass in the
left hemithorax (Figure 1a). After a chest CT scan, there was revealed a large, 5.5 cm in diameter, multilobar
mass attached to the upper lobe of the left lung, extending into the left lung, touching
the cardiac wall and invading the pericardial fatty tissue, without infiltrating the
parenchyma of neither the lung nor the heart (Figure 1b). The CT imaging of the abdomen showed no signs of lymph node enlargement or any
metastatic disease. Subsequently, a biopsy of the tumour was conducted, through an
FNA CT-scan. The histological results revealed a hyperplasia of the lymphoid tissue.

Following these, the patient was scheduled for surgery. She was operated on through
a posterolateral thoracotomy in the 5th left intercostal space. A 5 × 6 × 4.5 cm tumour was found with a pedicle stemming
from the visceral pleura of the upper lobe of the left lung anteriorly. It was "touching"
the wall of the left lung and heart, obscuring the pericardia fatty tissue. There
were no signs of the tumour infiltrating the lung or any of the adjacent structures.
Note that the only connection of the tumor with the lung was its pedicle and that
there was no connection of the tumour with the mediastinum and the thymus. Consequently,
the pedicle was sutureligated, divided and removed (Figure 2).

Figure 2.Thymoma after removed from the anterior periviscelar pleura of the left lung.

The postoperative course was uneventful and the patient was released from the hospital
on the 5th post-operative day. The anatomopathological examination of the sample using
optical microscopy and immunohistochemical tests confirmed the diagnosis of an ectopic
thymoma (Figure 3a, 3b). The resected specimen was a solid and elastic multi-lobulated, grey mass, with
a thick fibrous capsule. The microscopy showed nodules of varying sizes comprising
a mixture of polygonal, ovoid and spindle (epithelial) cells, associated with a dense
lymphoplasmacytic infiltrate, vascular proliferation, nuclear pleomorphism, scanty
mitoses, but no tumour giant or necrotic cells. These histopathologic findings were
consistent with a type AB according to World Health Organization Classification System
(1999) and the pathologic stage was stage I on the classification system of Masaoka
(Table 1) [1,7,8].

Discussion

The thymus gland is an anterior mediastinal structure arising embryologically from
the third, and to a lesser extent, the fourth pharyngeal pouch. A prominent organ
early in life, the thymus reaches a maximum size of 40 g during puberty before regressing
and involuting during adulthood, being replaced by fibro-fatty tissue [1]. Thymoma is an uncommon neoplasm that derives from the epithelial cells of thymus
and it is the most common neoplasm of the anterior mediastinum, most frequently found
in adults at their 40 s. Nevertheless, cases of ectopic thymomas have been found in various locations, as it has already mentioned [1-6].

Furthermore, the thymomas have many interesting clinical features, such as their unique
association with myasthenia gravis or autoimmune diseases (as pancytopenia, hypogammaglobulinemia).
Approximately 35% of thymoma patients have myasthenia gravis, while 5%-10% have other
systemic syndromes [1,8]. Moreover, in the case of an ectopic thymoma, the possibility of solitary metastases
from a small undetected primary tumour in the thymus should be considered [8,9].

The majority of the patients suffering from thymoma are asymptomatic. However, when
clinical symptoms are present, they can roughly be differentiated between localizing symptoms, and systemic symptoms, due to the release of excess hormones, antibodies, and cytokines [1,8,9]. The most common clinical symptoms are cough (60%), chest pain (30%), fevers/chills
(20%) and dyspnea (16%) [1,8,9]. Myasthenia gravis patients are characterized by the development of autoimmune antibodies
to the acetylcholine receptor on postsynaptic neuromuscular junctions. These antibodies
could be detected with blood tests [8].

Nevertheless, imaging is an essential part of the workup and in conjunction with history
and physical exam is often the only investigation needed prior to treatment [1]. Following identification of a mass on chest x-ray, a CT scan of the chest should
be obtained, as it allows for the characterization of tumors as well as an assessment
of possible invasion into surrounding structures [10]. Dynamic magnetic resonance imaging (MRI) has been examined as a potential way to
improve staging and differential diagnosis determination [11], and PET has been examined for tumor detection and differentiation between invasive
and noninvasive thymoma with mixed results [12].

The thymomas can be classified according to the degree of invasion of the tumor through
the capsule into the surrounding structures (Masaoka staging system - the most widely accepted) or according to the morphology of the epithelial cells
and the lymphocyte-to-epithelial cell ratio (WHO system) [7-9]. Surgical resection is the standard of care for both non-invasive and invasive thymomas
as it provides the best prognosis [13]. For locally invasive or metastatic disease, or inoperable tumors, adjunctive therapy
is used, which may include chemotherapy and radiation treatment [1,8,9,13].

Completely resected, Masaoka stage II and III thymomas may benefit from adjuvant radiotherapy
to reduce local recurrence rates, but without impact on survival. In primary unresectable
thymomas, multimodal strategy nowadays includes neo-adjuvant chemotherapy, extensive
surgery, adjuvant radiotherapy, and in some cases, adjuvant chemotherapy. The most
popular chemotherapy regimens combine cisplatin, adriamycin, etoposide, cyclophophamide,
or ifosfamide [14,15].

Due to thymomas rarity, the most chemotherapeutic trials are case reports or phase
II trials, while prospective randomized trials are not available, so as to compare
the different chemotherapeutic agents. Nevertheless, the most commonly employed drug
in combination chemotherapy of thymomas is cisplatin and several studies reported
responses in excess of 50% with these combinations [8,13-15].

Conclusion

Ectopic thymoma is an uncommon neoplasm. To our knowledge, a case of an ectopic thymoma
stemming from the visceral pleura of the lung is extremely rare.

Consent

Written informed consent was obtained from the patient for publication of this case
report and accompanying images. A copy of the written consent is available for review
by the Editor-in-Chief of this journal.

Competing interests

The authors declare that they have no competing interests.

Authors' contributions

KS conducted a literature search, prepared the final manuscript and operated the patient.
DDN conducted a literature search, contributed to the preparation of the manuscript
and operated the patient. MK prepared the first draft of the manuscript and treated
the patient. CK, SS and MP supervised the manuscript, examined and treated the patient.
KS, DDN and KM participated in the surgical operation, and contributed equally in
the post-operative patient's follow-up. All authors contributed in collecting patient
data and editing arthroscopic operative images. All authors read and approved the
final manuscript.

Acknowledgements

We thank Andreas Moutsios-Rentzos for helping us with the editing of this case study.